Contesting in the general elections for the first time from Polonnaruwa District he entered the Parliament on 15th February 1989 from the Sri Lanka Freedom Party (SLFP).

He obtaining the highest number of preferential votes from Polonnaruwa District contesting the general election 1994, he was appointed the Deputy Minister for Irrigation. The Cabinet portfolio of Mahaweli Development and Parliamentary Affairs was given him in 1997 and was elected as the General Secretary of the SLFP in 2001.

In 2004 he was also appointed as the Leader of the House of Parliament. The Cabinet portfolios of Agriculture, Irrigation and Mahaweli Development, Environment & Natural Resources were given to him in 2005. He became the Cabinet Minister for Agricultural Development and Agrarian Services Development at the cabinet reshuffle in 2007.

Since 2005 at the height of the war in Sri Lanka, Minister Maithripala Sirisena functioned as the Acting Defence Minister of Sri Lanka on nine occasions. He was the acting Defence Minister in the final days of the war in Sri Lanka in the absence of the Defence Minister, the then President.

Minister Maithripala was elected once again to the parliament in 2010 and was appointed as the Cabinet Minister of Health of the UPFA government.

At the Presidential Election held on 8th January 2015, he was elected elected as the 6th Executive President of Sri Lanka.